The present invention relates generally to radar processing and more specifically, to a radar process and system for creating and maintaining the quality of a high resolution range profile for a target in the presence of jamming.
Modern radar systems having high resolution capability are useful in many situations, such as target detection, target discrimination, target recognition, and terrain imaging. Such radar systems are frequency agile and operate at rapidly varying frequencies. These radar systems are vulnerable to diverse threats such as intentional jamming, spoofing, and radar frequency interference (RFI). Also, in air and missile defense applications, the target platform may also comprise countermeasures such as jamming and chaff.
Of particular interest are systems having high resolution in range. The performance of high range resolution (HRR) systems is degraded in the presence of jamming interference. Typically, jamming is in the form of a high power transmission designed to impair a radar system""s performance. Jamming may comprise a signal modulated with noise or other disruptive information. The object of typical jammers is to impair the performance of a radar system""s receiving electronics and/or obscure display of potential targets of interest. The source of jamming interference may be mobile or may be relatively stationary (e.g., land based systems). HRR processing is vulnerable to interference due to jamming because it requires a relatively wide operational bandwidth, thus increasing the chances that a jammer at a particular frequency will be in the operational bandwidth. HRR processing is also vulnerable to jamming interference because of the relatively long coherent integration time associated with HRR processing. This increases the likelihood that a jammer will transmit while the HRR echoes are being received. Therefore, to avoid performance degradation due to jamming interference, it is desirable to eliminate jamming interference from the received signal (e.g., via cancellation, attenuation).
Jamming interference is typically cancelled by adaptively forming beam patterns, wherein nulls of the beam patterns are steered in the direction of the source(s) of jamming interference. Many existing adaptive techniques require a training period in which a signal is not present (such as during a passive listening period), or a period in which the signal value is low compared to jamming interference (such as in a search radar system) in order to distinguish signal energy from jammer energy. However, during HRR processing, signal content is available in all frequency samples. Thus, conventional adaptive techniques may cancel desired signal content in addition to canceling jamming interference. Also, conventional adaptive techniques tend to modulate the signal of interest, causing degradation in sidelobe performance, as a result of changing adaptive weight values. Thus, conventional adaptive techniques may degrade the image quality of an HRR profile.
Wideband jamming cancellation, in conjunction with stretch processing, was introduced in a document entitled xe2x80x9cNulling Over Extremely Wide Bandwidths When Using Stretch Processingxe2x80x9d, proceedings of Adaptive Sensor Array Processing (ASAP), March 1999. The technique introduced in that document processed a wideband signal as a sequence of narrowband signals. However, this technique does not address the signal cancellation or the adaptive weight modulation problems described above. Thus a need exists for an HRR process that can create an HRR profile and maintain the quality of the profile in the presence of countermeasures.
A system and method for creating a high resolution range (HRR) profile for a radar target of interest in the presence of jamming interference include transmitting an HRR waveform and receiving an echo signal resulting from the transmitted HRR waveform. Beam patterns are formed for each echo signal segment of the echo signal such that at least one null of each beam pattern is steered toward at least one interference and a frequency dependent gain of each beam pattern is maintained toward the center of the target of interest. The HRR profile is created from the beam patterns.